Spectro-Photometer for the History of the Universe, Epoch of Reionization, and Ices Explorer, One Quarter Scale Prototype Thermal Testing

The SPHEREx instrument has been proposed as a NASA Small Explorer (SMEX) mission designed to perform an all-sky near-infrared survey. The primary science objective of the SPHEREx instrument is the mapping and cataloging of data on galaxy red shifts and absorption spectra. The SPHEREx instrument utilizes a linear variable band pass filter to provide discrete spectral coverage of the 0.75μm to 5.0μm rage. The nominal on-orbit mission lifetime for the instrument is 2 years with continuous primary science imaging. The SPHEREx instrument will be placed in a near-circular LEO sun-synchronous terminator orbit with a mean altitude of 600 km, and solar beta angles ranging from 59° to 90°.

A passive v-groove radiator cooling system was selected for the SPHEREx instrument. This design was chosen for its simplicity and lack of vibration. It includes five radiator stages with the coldest two stages providing temperatures below 80K and 55K for the 2.3μm and 5.3μm detectors respectively.

A ¼ scale thermal prototype was constructed to characterize the performance of the SPHEREx thermal control system. This prototype was directly derived and scaled from the current flight design, and accurately replicates all heat flow paths at scale. The prototype was tested in a flight-like environment in the Cryogenic Systems Engineering, Advanced Thermal Technology Lab at NASA’s Jet Propulsion Laboratory. The testing simulated two test conditions, with the second exploring the maximum heat loads that could be applied to the 55K radiator stage while still meeting science requirements.

Following testing, a previously developed ¼ scale thermal model was correlated to the two conditions seen in test. The resultant correlated model is able to predict the prototype test temperatures to within 2K for all critical radiator stages. An overview of the thermal control design approach, the test configuration, and test and correlation results are presented.